XR650R and High compression piston


20 replies to this topic
  • hondacrf150f1

Posted February 01, 2008 - 09:01 AM

#1

I was looking over XR's Only yesterday and noticed that they offer a 12:1 compression piston. I think the HRC kit only comes with a 11:1. So anyway here is my question.

In the near future i would like to rebiuld my 650R with a 11:1 or 12:1 compression piston, from XR's only you can get the full piston, rings, and everything you need to rebiuld for $210...but the cam cost $800:crazy: I mean thats all thats in the HRC kit right? piston and cam? Will the bike run right with a 11:1 or 12:1 piston and the stock cam?

  • Thumpmeister

Posted February 01, 2008 - 09:45 AM

#2

Basically those are the two main components of the HRC kit, however there are a lot of other parts that go into it too, like clutch springs, and so on.

http://www.thumperta...ad.php?t=596472

You can basically make your own 'powerup kit' for less than half the cost of the Honda one, thats kind of what I've found after talking to different people on here. Buy a high comp piston like your talking about, and then get a cam like a Hotcam stg 1 or 2, and you're set.

  • Denn10

Posted February 01, 2008 - 09:47 AM

#3

Since im a L guy whats stock compression of a R?

  • Thumpmeister

Posted February 01, 2008 - 09:49 AM

#4

Someone might correct me on this, but I think its either 10:1, or 10.5:1.

  • martinfan30

Posted February 01, 2008 - 10:06 AM

#5

10:1...

http://www.cyclechao...ki/Honda_XR650R

  • resurrection

Posted February 01, 2008 - 10:23 AM

#6

I'v read that the high comp piston is detramental to top speed.

Dirt bike mag in 02/03 had agreat artical on how fast do you wont to go .

They got 125 mph the fastest of the bikes in test was R model .YA BABY
I must have read it 10 times.

  • XR4DEZ

Posted February 01, 2008 - 10:34 AM

#7

When Honda ran the 650r they opted not to use the high compression piston and stick with stock to keep from having to use race fuel.

  • Denn10

Posted February 01, 2008 - 11:09 AM

#8

10-1 stock if fairly good, definitely going to 11-1 prolly not alot of gain. I can see why alot of R guys dont change it since its not low like a L.

  • XRMANU

Posted February 01, 2008 - 12:13 PM

#9

Hotcams stage 1??

  • hondacrf150f1

Posted February 01, 2008 - 12:47 PM

#10

When Honda ran the 650r they opted not to use the high compression piston and stick with stock to keep from having to use race fuel.


I've known a bunch of guys who run regular 87 in todays MX bikes, my friend runs 87 in his CRF250R and that thing is 12:9 compression, so why couldnt you just run it in a 11:1 or 12:1 on a 650R?

His bike ran awsome with regular to.

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  • Denn10

Posted February 01, 2008 - 01:14 PM

#11

I've known a bunch of guys who run regular 87 in todays MX bikes, my friend runs 87 in his CRF250R and that thing is 12:9 compression, so why couldnt you just run it in a 11:1 or 12:1 on a 650R?

His bike ran awsome with regular to.


Just dont think that cuz you see one that works that everyone will, There are some different things that can differ in head design and all that can affect it differently between all bikes.

stock 10-1 to an upgrade to 11-1 wont be alot of difference, but if your thinking about all this there may be some other mods like a defferent cam that will help with more flow and more HP. Some other mods may give you what kind of performance gains that you are desiring without a HIGHER than comp piston than you already have. Just some food for thought!

  • knuklehead

Posted February 01, 2008 - 02:19 PM

#12

HRC kit come's with HD timing chain,sprocket's and guide's I belive

  • XR4DEZ

Posted February 01, 2008 - 06:33 PM

#13

I've known a bunch of guys who run regular 87 in todays MX bikes, my friend runs 87 in his CRF250R and that thing is 12:9 compression, so why couldnt you just run it in a 11:1 or 12:1 on a 650R?

His bike ran awsome with regular to.


The HRC manual specs race fuel, my 600 pinged without it. I've kept my 650 motor stock so it'll run on anything found in Mexico.

  • Maroast

Posted February 01, 2008 - 07:20 PM

#14

I've known a bunch of guys who run regular 87 in todays MX bikes, my friend runs 87 in his CRF250R and that thing is 12:9 compression, so why couldnt you just run it in a 11:1 or 12:1 on a 650R?
His bike ran awsome with regular to.



The kawasaki 250 ninja has 12.4:1 compression and that thing would run fine on a mixture of 1/2 85 octane, 1/2 urine.

Like Denn10 said, I believe there are a lot of dynamic factors involved that would lead to pre-detonation in one engine and not in another.

I'm not going to lie and tell you i know, but I think one factor you have to look at is the surface area of a piston in relation to compression and the resulting thermal dynamics. The 250 ninja has two 125cc piston cranked up to 12.4:1 and it runs fine on dirty pump gas.... but a lot of the dudes around here say they can get some pretty nasty pinging out of their 11:1 650r.

I would love to hear an explanation of this from one of our many resident motor builders here.... Stepho, paging Stepho

  • kingsman

Posted February 01, 2008 - 08:37 PM

#15

first I ask y reg?? for a few cents more you can buy 97! burns cleaner, more power, hens longer life spand!! so pump with 10:1 is fine but when ever you mod a motor you mod your fuel!! mods meen aluminum pistons, port polish.... now you have more things to think of.. " hmm do i really want carbon build up on that $200. piston or thrue my $600. port job.... hell no, so you run a mix, 50/50 some 97 and some 110 or if your down, strait 110!!

it's not that your bike wont run on pump, its how long do you want your built bike to run!!

Rider of: trx450r, crf450r, xr650r, cr500, trx250r and a crf50> lol

  • hondacrf150f1

Posted February 02, 2008 - 05:16 AM

#16

first I ask y reg?? for a few cents more you can buy 97! burns cleaner, more power, hens longer life spand!! so pump with 10:1 is fine but when ever you mod a motor you mod your fuel!! mods meen aluminum pistons, port polish.... now you have more things to think of.. " hmm do i really want carbon build up on that $200. piston or thrue my $600. port job.... hell no, so you run a mix, 50/50 some 97 and some 110 or if your down, strait 110!!

it's not that your bike wont run on pump, its how long do you want your built bike to run!!

Rider of: trx450r, crf450r, xr650r, cr500, trx250r and a crf50> lol


So does your 650R have a high comp piston in there??? And where the hell can you get 97...out here in the northeast the highest is 93, and 94 at sunoco. And 87 to 93 is a 30 cent per gallon jump...whats 100 or 110 gas gona cost? $5-$7 a gallon?

  • martinfan30

Posted February 02, 2008 - 08:17 AM

#17

The way I see it is, that the 30 cent jump from reg. to supreme would only be a total of .90 to fill a 3 gal. tank.

I can live with that.

  • Thumpmeister

Posted February 02, 2008 - 09:10 AM

#18

The way I see it is, that the 30 cent jump from reg. to supreme would only be a total of .90 to fill a 3 gal. tank.

I can live with that.


Thats the way I look at it too. Spend a dollar extra, and get better performance.

  • Billahjack

Posted February 02, 2008 - 09:23 AM

#19

I've known a bunch of guys who run regular 87 in todays MX bikes, my friend runs 87 in his CRF250R and that thing is 12:9 compression, so why couldnt you just run it in a 11:1 or 12:1 on a 650R?

His bike ran awsome with regular to.


Bore size affects octane rating requirements due to the geometry and tendancy to cause detonation. I don't know the exact specifics, but I do know that the 650R has a huge bore compared to a CRF250R or ninja 250 twin cylinder.

In the car arena, Honda car motors tend to have a longer stroke than bore to run high compression on normal gas. Subaru motors have a bigger bore than stroke and can not run too high of compression or turbo boost without detonation problems unless they run high octane fuel.

  • weskc35k

Posted February 03, 2008 - 12:36 AM

#20

My bike likes 98 octane fuel with Ethanol at 10% in it for some reason,i know it shouldn't but it does.





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